gh-120492: Sync importlib_metadata 8.2.0 (#124033)

* Sync with importlib_metadata 8.2.0

Removes deprecated behaviors, including support for `PackageMetadata.__getitem__` returning None for missing keys and Distribution subclasses not implementing abstract methods.
Prioritizes valid dists to invalid dists when retrieving by name (python/cpython/#120492). Adds SimplePath to `importlib.metadata.__all__`.

* Add blurb

Lib/test/test_importlib/metadata/test_api.py

@@ -1,9 +1,7 @@
 import re
 import textwrap
 import unittest
-import warnings
 import importlib
-import contextlib
 
 from . import fixtures
 from importlib.metadata import (
@@ -18,13 +16,6 @@
 )
 
 
-@contextlib.contextmanager
-def suppress_known_deprecation():
-    with warnings.catch_warnings(record=True) as ctx:
-        warnings.simplefilter('default', category=DeprecationWarning)
-        yield ctx
-
-
 class APITests(
     fixtures.EggInfoPkg,
     fixtures.EggInfoPkgPipInstalledNoToplevel,
@@ -153,13 +144,13 @@ def test_metadata_for_this_package(self):
         classifiers = md.get_all('Classifier')
         assert 'Topic :: Software Development :: Libraries' in classifiers
 
-    def test_missing_key_legacy(self):
+    def test_missing_key(self):
         """
-        Requesting a missing key will still return None, but warn.
+        Requesting a missing key raises KeyError.
         """
         md = metadata('distinfo-pkg')
-        with suppress_known_deprecation():
-            assert md['does-not-exist'] is None
+        with self.assertRaises(KeyError):
+            md['does-not-exist']
 
     def test_get_key(self):
         """